Glyceraldehyde-3-Phosphate Dehydrogenase in Retinal Microvasculature: Implications for the Development and Progression of Diabetic Retinopathy

Abstract

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been hypothesized as a mediator in the activation of multiple pathways implicated in the pathogenesis of diabetic retinopathy. The objective of this study was to understand the mechanism by which high glucose inactivates GAPDH in retinal microvascular cells. Bovine retinal endothelial cells (BRECs), transfected with GAPDH, were incubated in 20 mM glucose. The effect of the overexpression of GAPDH on its activity, apoptosis, and upstream signaling pathways, protein kinase C, and hexosamine pathways was determined. The effect of the inhibitors of nitration and ribosylation on GAPDH activity, its nuclear translocation and reversal of glucose insult was also evaluated. High glucose decreased GAPDH activity, expression, and nuclear translocation. Overexpression of GAPDH prevented glucose-induced inhibition of its activity, nuclear translocation, apoptosis, and activation of protein kinase C and hexosamine pathways. Inhibitors of nitration and ribosylation ameliorated glucose-induced inhibition of GAPDH, and their addition during the normal glucose exposure that followed high glucose levels had a beneficial effect on GAPDH activity and the degree of nitration and ribosylation. In hyperglycemia, GAPDH in retinal microvascular cells is inhibited by its covalent modifications, and this activates multiple pathways implicated in the pathogenesis of diabetic retinopathy. The agents that can directly target modification of GAPDH have potential in inhibiting the development and in arresting the progression of diabetic retinopathy.